Fix True-Name Nemesis chosen-player protection

crates/engine/src/game/keywords.rs

@@ -542,6 +542,11 @@ pub fn source_matches_protection_target(
             .chosen_card_type()
             .and_then(|ct| ct.protection_quality_str())
             .is_some_and(|quality| source_matches_card_type(source, quality)),
+        // CR 702.16 + CR 109.4: the source is protected against objects
+        // controlled by the player chosen for the protected permanent.
+        ProtectionTarget::ChosenPlayer => protected
+            .chosen_player()
+            .is_some_and(|player| source.controller == player),
         // CR 702.16j: "Protection from everything" — protection from each object
         // regardless of the source's characteristic values.
         ProtectionTarget::Everything => true,

crates/engine/src/game/static_abilities.rs

@@ -1654,6 +1654,7 @@ pub fn player_protection_from(
                 // a player; object-level grants of these qualities flow through the
                 // `AddKeyword(Protection)` continuous path, not `PlayerProtection`.
                 ProtectionTarget::ChosenColor
+                | ProtectionTarget::ChosenPlayer
                 | ProtectionTarget::Color(_)
                 | ProtectionTarget::Multicolored
                 | ProtectionTarget::Quality(_)

crates/engine/src/types/keywords.rs

@@ -502,6 +502,9 @@ pub enum ProtectionTarget {
     /// resolved at runtime from the source permanent's `chosen_attributes`
     /// (the `CardType` chosen as the permanent entered). Parallels `ChosenColor`.
     ChosenCardType,
+    /// CR 702.16 + CR 109.4: "Protection from the chosen player" — resolved
+    /// at runtime from the protected permanent's persisted player choice.
+    ChosenPlayer,
     /// CR 702.16j: "Protection from everything" — protection from each object
     /// regardless of that object's characteristic values. Matches every source
     /// in `source_matches_protection_target`.
@@ -2883,6 +2886,9 @@ pub(crate) fn parse_protection_target(s: &str) -> ProtectionTarget {
         // CR 702.16 + CR 205.2: "the chosen card type" resolves at
         // runtime from the source permanent's chosen `CardType` attribute.
         "the chosen card type" | "chosen card type" => ProtectionTarget::ChosenCardType,
+        // CR 702.16 + CR 109.4: "the chosen player" resolves from the
+        // protected permanent's persisted `ChosenAttribute::Player`.
+        "the chosen player" | "chosen player" => ProtectionTarget::ChosenPlayer,
         // CR 702.16j: "protection from everything" — typed variant, not stringly-typed
         "everything" => ProtectionTarget::Everything,
         // CR 702.16k: "protection from each of your opponents" (Figure of
@@ -4104,6 +4110,22 @@ mod tests {
         );
     }
 
+    #[test]
+    fn parse_protection_target_chosen_player() {
+        assert_eq!(
+            parse_protection_target("the chosen player"),
+            ProtectionTarget::ChosenPlayer
+        );
+        assert_eq!(
+            parse_protection_target("chosen player"),
+            ProtectionTarget::ChosenPlayer
+        );
+        assert_eq!(
+            Keyword::from_str("Protection:the chosen player").unwrap(),
+            Keyword::Protection(ProtectionTarget::ChosenPlayer)
+        );
+    }
+
     /// CR 702.16a + CR 202.3: "mana value N or less/greater" parses to
     /// `ProtectionTarget::Filter` with a `Cmc` property.
     #[test]

crates/engine/tests/integration/issue_5941_true_name_chosen_player_protection.rs

@@ -0,0 +1,63 @@
+//! Issue #5941: True-Name Nemesis must not be targetable by objects controlled
+//! by the player chosen as it entered the battlefield.
+//!
+//! The regression drives the parsed ETB choice through `ChooseOption`, then
+//! checks the production target-legality predicate with sources controlled by
+//! both players.
+
+use engine::game::scenario::{GameScenario, P0};
+use engine::game::targeting::find_legal_targets;
+use engine::types::ability::ChoiceType;
+use engine::types::ability::TargetFilter;
+use engine::types::actions::GameAction;
+use engine::types::game_state::WaitingFor;
+use engine::types::identifiers::ObjectId;
+use engine::types::player::PlayerId;
+
+const P1: PlayerId = PlayerId(1);
+const TRUE_NAME_ORACLE: &str = "As True-Name Nemesis enters, choose a player.\nTrue-Name Nemesis has protection from the chosen player. (This creature can't be blocked, targeted, dealt damage by, or enchanted by anything controlled by that player.)";
+
+fn add_source(scenario: &mut GameScenario, player: PlayerId, name: &str) -> ObjectId {
+    scenario.add_creature(player, name, 2, 2).id()
+}
+
+#[test]
+fn true_name_protection_uses_the_protected_objects_chosen_player() {
+    let mut scenario = GameScenario::new_n_player(2, 5941);
+    let true_name = scenario
+        .add_creature_from_oracle(P0, "True-Name Nemesis", 3, 1, TRUE_NAME_ORACLE)
+        .id();
+    let chosen_player_source = add_source(&mut scenario, P1, "Song of the Dryads");
+    let other_player_source = add_source(&mut scenario, P0, "Friendly Spell");
+    let mut runner = scenario.build();
+
+    let source = crate::support::exact_named_choice_source(runner.state(), true_name);
+    runner.state_mut().waiting_for = WaitingFor::NamedChoice {
+        player: P0,
+        choice_type: ChoiceType::player(),
+        options: vec![P0.0.to_string(), P1.0.to_string()],
+        source: Some(source),
+        persist_player: None,
+    };
+    runner
+        .act(GameAction::ChooseOption {
+            choice: P1.0.to_string(),
+        })
+        .expect("choosing the player must succeed");
+
+    assert_eq!(runner.state().objects[&true_name].chosen_player(), Some(P1));
+
+    let targets_from_chosen_player =
+        find_legal_targets(runner.state(), &TargetFilter::Any, P1, chosen_player_source);
+    assert!(
+        !targets_from_chosen_player.contains(&engine::types::ability::TargetRef::Object(true_name)),
+        "True-Name must not be targetable by the chosen player's source, got {targets_from_chosen_player:?}"
+    );
+
+    let targets_from_other_player =
+        find_legal_targets(runner.state(), &TargetFilter::Any, P0, other_player_source);
+    assert!(
+        targets_from_other_player.contains(&engine::types::ability::TargetRef::Object(true_name)),
+        "True-Name must remain targetable by another player's source, got {targets_from_other_player:?}"
+    );
+}

crates/engine/tests/integration/main.rs

@@ -635,6 +635,7 @@ mod issue_5900_conjurers_mantle;
 mod issue_5901_depthshaker_titan;
 mod issue_5902_heart_shaped_herb;
 mod issue_5910_kitchen_finks_persist;
+mod issue_5941_true_name_chosen_player_protection;
 mod issue_5945_kellan_the_kid;
 mod issue_5946_pest_infestation_bogwater_softlock;
 mod issue_5963_scavengers_talent_food_sacrifice;